1. Field of the Invention
This invention relates to a vibrating apparatus for vibrating a flask to compact molding sand in the flask, and in more detail, to an improvement of a vibrating apparatus for vibrating a flask to compact molding sand in the flask that is provided with an elastically supported vibrating table on which the flask is mounted and with unbalanced-weight-type vibrating motors mounted on the vibrating table for vibrating it by rotating the unbalanced weights of the motors.
2. Description of the Prior Art
In conventional evaporative pattern casting, which uses molding sand that includes no binder, or in conventional molding for producing a self-hardening mold, which uses molding sand that includes a small amount of binders, a vibrating table is used for vibrating a flask to satisfactorily and efficiently compact molding sand in the flask.
Such a vibrating table must cause the molding sand to move circularly to satisfactorily and efficiently compact it when the flask is vibrated. A vibrating device for circularly moving the molding sand to compact it is proposed in JP 10-328783, A. The vibrating device as shown in the Japanese patent gazette includes two unbalanced-weight-type motors mounted on a vibrating table at the sides of a flask placed on the vibrating table, with the axes of rotation of the motors being arranged in parallel at the level of the centroid of the flask.
However, in the conventional vibrating device for compacting molding sand, which is configured as described above, in fact the two unbalanced weights rotate out of phase, resulting in a phase difference between them. The phase difference causes a problem in that the vibrating table cannot move in a required circular motion since it oscillates laterally.
This invention has been conceived to overcome that problem. Its purpose is to provide a vibrating apparatus for compacting molding sand that can eliminate the oscillation of the vibrating table.
The vibrating apparatus of the present invention for vibrating a flask to compact molding sand in it included an elastically supported vibrating table on which the flask can be placed, and two unbalanced-weight-type motors mounted on the vibrating table for vibrating it by rotating the unbalanced weights of the motors. The two motors are disposed above the vibrating table at the sides of the flask. The axes of rotation of the motors are located on a horizontal line that substantially passes the centroid of the entire elastically supported vibrating apparatus, including the vibrating table, the two motors, the flask, mad molding sand in the flask. Further, the unbalanced weights of the motors are rotated at the same speed in one direction.
If there is a phase difference between the unbalanced weights when they are rotated at the same speed in one direction by the two motors, the rotation moment of the two unbalanced weights is less than that when there is no phase difference, as shown in FIG. 1. In FIG. 1, F denotes the centrifugal force of one unbalanced weight, and L denotes the radius of rotation of both weights. FIG. 2 shows the rotation moment of the unbalanced weights when the phase difference varies between them. If the common axis of rotation of the motors does not coincide with the centroid of the entire vibrating apparatus, the apparatus would oscillate laterally. However, in the vibrating apparatus of the present invention the length of the arm of the rotation moment that accounts for the lateral oscillation is zero. Therefore, the rotation moment that accounts for the lateral oscillation will also be zero.
In one aspect of the invention, the vibrating apparatus includes means for adjusting the vertical position of the two motors to have their axes of rotation coincide with the centroid of the entire vibrating apparatus when the position of the centroid changes.